OPINION — While President Trump complains about the national media, Democrats, Robert S. Mueller’s Russian “witch hunt” and the political establishment, none of those things is why the November House elections are a major headache for the Republican Party. Donald Trump’s biggest problem is Donald Trump.

Trump has turned what could have been a challenging midterm election environment into a potentially disastrous one. Through his tweets and statements, the president continues to make the 2018 midterm elections a referendum on his first two years in office.

Analysis — If you trust the July 9-11 Fox News poll and the July 15-18 NBC News/Wall Street Journal survey — and I have no reason not to — the GOP still looks headed for a difficult election and the likely loss of the House.

No, President Donald Trump’s voters are not fleeing him, and his personal poll numbers have not cratered even after his behavior at the NATO summit in Belgium and his Helsinki meeting with Vladimir Putin. So, maybe he really could shoot someone on Fifth Avenue and not lose any voters. But that says something about Trump’s supporters, not the overall electorate.

Commenting after President Donald Trump’s performance in Helsinki, Senate Majority Leader Mitch McConnell observed, “I have said a number of times, I’ll say it again: The Russians are not our friends. And I entirely believe the assessment of our intelligence community.”

Tennessee Republican Sen. Lamar Alexander said in a release, “There is no doubt that Russia interfered in our 2016 presidential election.”

The selection of Brett Kavanaugh for the Supreme Court will have less of an impact on November’s midterms than you think. Sure, depending how the confirmation process develops, it’s possible the nomination could affect a handful of races, but the most likely scenario will not change the overall trajectory of the November elections.

The most likely outcome of the Kavanaugh nomination involves all 50 Republican senators voting to confirm him to the Supreme Court (with John McCain not voting).

You need to hand it to President Donald Trump, his entire administration and his party. It takes more than a little chutzpah to act in a way that seems callous to the concerns of children. First, it was gun control. Now it is immigration in general, and separating children from their parents in particular. If this is the way to winning the midterms, it’s hard to see how.

Republicans have talked for decades about crime, drugs, national security, traditional values, the dangers associated with big government and helping businesses produce economic growth.

While many dissected Corey Stewart’s recent Virginia Republican Senate primary victory and South Carolina Rep. Mark Sanford’s defeat in his bid for renomination, an even more interesting runoff race is underway in the Palmetto State.

The June 12 Republican primary in Trey Gowdy’s open 4th District seat produced a runoff pitting first-place finisher Lee Bright, a former state senator, against William Timmons, a first-term state senator.

For the last couple of months, I’ve heard from many quarters that the “blue wave” has dissipated. Meh.

Advocates of that view usually point to the RealClearPolitics generic ballot average or Donald Trump’s job approval ratings, which suggest the president’s popularity has risen and the Democratic House advantage fallen.

Former Trump campaign chief executive and White House strategist Steve Bannon recently told CNN’s Fareed Zakaria that the midterm elections will be “an up or down vote” on the president. He also asserted that it’s imperative that Donald Trump nationalize the midterm elections.

“Trump’s second presidential race will be on Nov. 6 of this year. He’s on the ballot, and we’re going to have an up or down vote. Do you back Trump’s program, OK, with all that’s good and all that’s bad? Do you back Trump’s program, or do you back removing him?” Bannon told Zakaria.

I don’t trust anyone who tells me they already know the makeup of the midterm electorate. We can’t possibly know who will vote in the fall, let alone how they will cast their ballots.

If I were going to focus on a handful of variables to understand how the cycle is unfolding, I’d certainly pay close attention to partisanship. But instead of focusing primarily on the percentage of Republicans and Democrats among voters, I’d pay more attention to the attitudes (and then the behavior) of self-identified independents.

President Donald Trump, who preaches pro-business policies at home and more favorable terms for the United States in trade deals, may well help elect more anti-American leaders around the world and leave the United States more isolated and embattled.

We could see the first manifestation of this in Trump’s confrontational approach with Mexico. His positions on trade (particularly the North American Free Trade Agreement) and immigration, and his characterization of the people of Mexico, have boosted the prospects of presidential hopeful Andrés Manuel López Obrador in Mexico’s July 1 election.

Every election cycle, at least a few “semi-celebrities” (or those with connections to semi-celebrities) run for office. This cycle is no exception.

Actress Cynthia Nixon of “Sex in the City” fame is running for the Democratic nomination for governor of New York, while Greg Pence, the vice president’s brother, won the Republican nomination in Indiana’s 6th District.

Yes, it’s time for another of my “dangerous dozen open House seats” columns, which I have been writing since shortly after the establishment of the Jamestown Settlement (or so it seems).

This cycle’s version has a plethora of seats to choose from, given the 38 Republican and 19 Democratic seats where an incumbent is not seeking re-election, either because he or she is retiring or running for a different office. (The number does not include those districts where a special election has already filled a vacancy or will be held before November.)

When this election cycle began, handicappers repeatedly pointed out that 10 Democratic Senate incumbents from states carried by Donald Trump would be on the ballot in 2018. That count was accurate, and the point behind it obvious — Republicans had a long list of opportunities.

But now even the most partisan Republicans are acknowledging that the list of serious targets is shrinking to five or six states. Indiana, Missouri, West Virginia, North Dakota and Florida are certainly in play, but how are the other competitive Senate races holding up?

Two early surveys show former Tennessee Gov. Phil Bredesen, a Democrat, holding a lead over Republican Rep. Marcia Blackburn in hypothetical ballot tests of this year’s Senate race.

Those polls, along with kind words about Bredesen from retiring Tennessee GOP Sen. Bob Corker, have raised the contest’s profile and heightened the buzz. But it’s best to be cautious about the former governor’s prospects as you watch the race play out.

In my column last week, I noted that current public opinion data and recent election results point to a likely Democratic takeover of the House in the fall.

Some argue President Donald Trump’s unpopularity is already baked into the election cake, leaving Republicans little room to maneuver. But if you are a GOP strategist or ally of the president, you still need to formulate a plan to improve your party’s prospects and even look toward 2020.

With President Donald Trump’s mediocre job ratings, Democrats’ advantage on the national generic ballot and success in special elections in Pennsylvania, Alabama and elsewhere, there’s plenty of talk about a political wave. In this week’s Decoder, Roll Call elections analyst Nathan Gonzales, sitting in for David Hawkings, talks with Roll Call columnist Stuart Rothenberg about how many seats it takes to make a wave and which Republicans might survive.